There are various forms of tropoelastin that typically appear to consist of two types of alternating domains: those rich in hydrophobic amino acids (responsible for the elastic properties) and those rich in lysine residues (responsible for cross-link formation). Hydrophobic and cross-linking domains are encoded in separate exons (Indik et al 1987).
The 26 A region of human tropoelastin is unique amongst tropoelastin domains in that, due to the absence of lysine, this region does not participate in elastin cross-link formation. Furthermore, this region is a serine-rich domain and lacks hydrophobic stretches, indicating that it is unlikely to contribute to the elasticity of tropoelastin. There is otherwise limited information on the structure and functional relationships of the 26 A region (Bedell-Hogan et al., 1993).
The gene for tropoelastin is believed to be present as a single copy in the mammalian genome, and is expressed in the form of multiple transcripts, distinguished by alternative splicing of the pre-mRNA (Indik et al, 1990; Oliver et al, 1987). Modest expression of a natural human tropoelastin sequence has been achieved by Indik et al (1990) using cDNA, providing free polypeptide which unfortunately was unstable.
Expression of substantial amounts of human tropoelastin using synthetic polynucleotides is reported in WO94/14958. In particular, a construct, SHEL, providing substantial amounts of full length human tropoelastin is described.